21081447 has 12 divisors (see below), whose sum is σ = 30499560. Its totient is φ = 14031888.

The previous prime is 21081443. The next prime is 21081491. The reversal of 21081447 is 74418012.

21081447 is a `hidden beast` number, since 210 + 8 + 1 + 447 = 666.

It is not a de Polignac number, because 21081447 - 2² = 21081443 is a prime.

It is a super-2 number, since 2×21081447² = 888854815227618, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21081447.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21081443) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5704 + ... + 8642.

It is an arithmetic number, because the mean of its divisors is an integer number (2541630).

Almost surely, 2^21081447 is an apocalyptic number.

21081447 is a deficient number, since it is larger than the sum of its proper divisors (9418113).

21081447 is a wasteful number, since it uses less digits than its factorization.

21081447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3742 (or 3739 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 27.

The square root of 21081447 is about 4591.4536913705. The cubic root of 21081447 is about 276.2486338596.

Adding to 21081447 its reverse (74418012), we get a palindrome (95499459).

It can be divided in two parts, 21081 and 447, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21081447 in words is "twenty-one million, eighty-one thousand, four hundred forty-seven".